Teletherapy is defined as a treatment methodology in which an irradiation source is at a distance from the body to be treated. X-rays and electron beams have long been used in teletherapy to treat various cancers. Unfortunately, X-rays exhibit a linear energy transfer approaching an exponential attenuation function, and are therefore of minimal safe use for deeply embedded growths. The use of heavy particles, particularly hadrons and more particularly protons, in teletherapy has found increasing acceptance, due to the ability of heavy particles to penetrate to a specific depth without appreciably harming intervening tissue. In particular, the linear energy transfer of hadrons exhibits an inversed depth profile with a marked Bragg peak defined as the point at which the hadrons deposit most of their energy, and occurs at the end of the hadrons path. As a result of this effect, increased energy can be directed at an embedded growth as compared to X-rays and electron beams, which particularly harm intervening tissues. While the term hadrons include a wide range of particles, practically, protons and various ions are most widely used in therapy. For clarity, this document will describe treatment as being accomplished with protons, however this is not meant to be limiting in any way.
The protons or ions can be focused to a target volume of variable penetration depth. In this way the dose profile can be matched closely to the target volume with a high precision. In order to ensure complete irradiation of the target growth, a plurality of beams arriving at the embedded growth from several different directions is preferred. The point at which the plurality of beams intersects, whether they are beamed sequentially or simultaneously, is termed the isocenter, and to maximize biological effectiveness the isocenter must be precisely collocated with the target growth.
Irradiation treatment is performed on a target tissue in a well defined process. In a first stage, known as the treatment planning stage, the target tissue is imaged and a treatment plan comprising dosage, patient position, and irradiation angles are defined. Furthermore, placement markers are defined, so as to ensure that subsequent irradiation sessions are properly targeted. Irradiation is then performed, responsive to the developed treatment plan, at a plurality of treatment sessions over a period of time, each session being known as a fraction. At each such fraction, care must be taken to ensure proper patient positioning, responsive to the placement markers, so as to avoid damage to organs in vicinity of the target tissue. Positioning of the patient responsive to the markers is performed based on visualization of the patient, responsive to the defined markers.
Particularly, during each fraction, the patient is positioned on a patient support member, such as a bed, in a setup position. The setup position is identical to the patient position during the imaging of the treatment planning stage, except that is in the treatment room and the center of the growth mass is positioned at the isocenter of the irradiation source. The setup position of the patient is optionally verified by imaging and/or positioning devices. Unfortunately, current irradiation systems are set up such that the setup position of the patient is always perpendicular to the central axis of the irradiation beam nozzle of the irradiation source. This limits the possibilities for patient positioning for better comfort or other constraints of the treatment room, especially when the irradiation source has a fixed position and is not moveable.